PCC problem, M51 is red

[chboing]

Hello,
This is the first time i have real problems with photometric color calibration.
I shot with RGB filters, integrated the preprocessed pictures, and trying to apply PCC is a total failure...
It does resolve the picture (m51, 1200mm, 1.9 pixel size drizzled) and it finally apply some color calibration, but it's not good at all ...
I would really like some help here because i'm a little lost.

here are some pictures and the 200Mb file.

https://www.dropbox.com/s/wxcqpuq5bjerh35/rgb_DBE_red.xisf?dl=0

ps:
-background neutralisation (before or while PCC) or not does not change anything
-psf photometry -> same result
-saturation does not look bad ...

[chboing]

One more attachement, showing the picture with link RGB channel desactivated.
Looks fine to me but i should have something like this with RGB channel linked right ?

[STEVE333]

I'll be glad to take a look at it.

Need your telescope focal length (including any effects of FR if present) and your pixel size to try PCC.

FYI I performed a BackgroundNeutralization + ColorCalibration on the image and it worked fine. The Red channel signal is quite a bit higher than the G and B channels, but, calibration took care of that.

Steve

[chboing]

Thank you Steve,
focal length is 1200 mm
pixel size is 3.8 but drizzled so 1.9 for pixel size
I'm not used to ColorCalibration, I'm a recent lazy photometric color calibration user 
I will take a look at that though, and i'd be glad if you manage to help me with PCC

[STEVE333]

Good news!

The first time I ran the PCC I also got a Red result.

However, if you check the typical value of the background of your image (before PCC) you will see that the R channel is about 0.12 or 0.13 which is higher than the default setting of 0.1 for the Upper limit in the Backlground Neutralization section. Thus, all of the R channel readings were discarded.

Solution: I raised the Upper limit value to 0.2 and ran PCC again. Everything then worked fine.

Hope this makes sense.

I have never run into this before, so, I learned something from your problem. Thanks for posting it.

Steve

[chboing]

Oh, that's it. I guess i could have tried to tweak this a bit, but that did not came to mind.
Thank you very much !

And by the way, your Messier collection is impressive, great job !

[STEVE333]

You're welcome. Glad I could help.

Thanks for the nice words about the Messiers.

• That was quite a journey that started with an ST-80 achromat on a NexStar 4SE Alt/Az mount. Exposures were limited to 30 sec, and, only about half of those were good enough to stack. In addition, all the images had blue halos around bright stars. My processing was with Photoshop CS2.
• I graduated to an iOptron ZEQ25 equatorial mount but remained unguided for a year or so. I was only able to extend the exposures to about 60 sec, but, it helped, and, most of the images were good enough to stack.
• At that time Frazzles loaned me an Orion ED-80 CF which greatly improved the quality of the images, but, still no guiding.
• Next I had my Canon T3 Baader modified to enhance the red sensitivity. That really helped with the Nebula images.
• Finally I started guiding and was able to extend exposure times to 3-5 minutes which definitely helped with the dimmer targets. Along came an Explore Scientific ED102 which helped with the smaller targets. I returned the Orion ED-80 to Frazzles with many thanks.
• After about another year I switched to PixInsight for processing, and, that was the software I used for the final Messier images. It is still the image processing software I use.
• After finishing the Messier 110 list I went on to get 40 of the "Southern Messier" objects (a list created in another forum).

I learned a lot during that journey, but, was glad to have it completed. Whewwwwww!

Anyway, hope your future processing goes smoothly.

All the best,

Steve

[chboing]

Quite the journey indeed, curious about the total time span of this

thank you again

[STEVE333]

I purchased BYEOS (to control my Canon DSLR) back in Aug 2013, so, that is when my journey started. I'm only 77 now, so, looking forward to many more years of astrophotography.

Enjoy,

Steve